Rapid gel formation in hydrocarbon recovery

ABSTRACT

Method and composition for gel formation in hydrocarbon recovery, in which an organic phosphate ester is gelled by a novel activator composition comprising iron sulfate, dibutylaminoethanol, and a phosphate surfactant.

TECHNICAL FIELD

This invention relates to hydrocarbon recovery, and in particular to theformation of gels useful in formation fracturing.

BACKGROUND OF THE INVENTION

In the recovery of hydrocarbons from underground formations, it iscommon to fracture the formations with fluids forced down a wellboreunder considerable pressure. Various types of fracturing fluids may beused. This invention is concerned with the use of hydrocarbon fracturingfluids, such as kerosene, Diesel oil, and the like. It is common toviscosify or gel hydrocarbon fracturing fluids so they are better ableto handle and distribute the propping agents commonly mixed with them.Propping agents such as sand or other relatively hard particulates areused to maintain the fissures in the formation after they are fractured,to assure the recoverable hydrocarbons in the formation are able to flowthrough the formation to be recovered.

It is desirable that the additives for the fracturing fluid should actrapidly and efficiently to make a useful--that is, a viscous--gel from asmall amount of chemical.

Dialkyl orthophosphates, particularly in the form of their aluminumsalts, have been used as components of hydrocarbon gelling agents formany years--see the generic description in Monroe's U.S. Pat. No.3,575,859, for example, issued in 1971. Monroe uses the dialkylphosphate esters in combination with alkyl and alkanol amines having upto 4 carbon atoms; he also uses certain polyamines. In U.S. Pat. No.4,153,649, Griffin lists eighteen U.S. patents said to teach thepreparation of phosphate esters useful in formation fracturing,incorporates them by reference, and goes on to discuss several others.More recently, McCabe, in U.S. Pat. No. 5,271,464, employs alkylorthophosphate esters with aluminum and iron compounds to make a gel; heuses them in combination with a monohydric alcohol having from 2 to 4carbon atoms and an alkyl or alkanol amine having from 8 to 18 carbonatoms. The gel is used as a temporary plugging agent. McCabe also, inEuropean Patent Application 0 551 021 A1, suggests a similar compositionas a fracturing agent.

Smith and Persinski (U.S. Pat. No. 5,417,287) suggest iron compounds incombination with orthophosphate esters to make a viscous hydrocarbonfracturing medium, and, in U.S. Pat. No. 5,614,010, include a lowmolecular weight amine and, optionally, a surfactant.

SUMMARY OF THE INVENTION

Our invention comprises compositions and methods for gelling hydrocarbonfracturing fluids. The composition comprises a phosphate esterpreferably neutralized with potassium hydroxide, dibutylaminoethanol,iron sulfate, and a phosphate surfactant, in the proportions describedherein.

The method includes adding the composition to a hydrocarbon fracturingfluid to create a viscous fracturing fluid. The invention furtherincludes a method of fracturing subterranean formation using the gelledhydrocarbon, with or without a proppant, under pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a computer printout showing gel stability of our invention at200° F. under two different revolutions per second of the FannViscometer.

FIG. 2 is similar to FIG. 1 but shows gel stability of a lowerconcentration of our activator.

FIG. 3 plots the close time for gels activated by our activator, usingincreasing amounts of KOH in the gelling agent.

FIG. 4 shows the crown time for our gels using increasing amounts ofKOH.

FIG. 5 shows the Marsh Funnel time for the gels of FIGS. 3 and 4.

DETAILED DESCRIPTION OF THE INVENTION

Our preferred method of viscosifying a hydrocarbon fracturing fluid isto employ two separate compositions--a phosphate ester which isneutralized by potassium hydroxide, and an activator.

The basic components of our new activator are, in parts by weight:

30-48 parts by weight iron sulfate

5-25 parts by weight dibutyl amino ethanol, and

5-20 parts by weight phosphate surfactant as described below. Dibutylamino ethanol is sometimes described herein as DBAE.

A preferred activator comprises, by weight, (a) about 50% to about 80%of a 60% solution of iron sulfate, (b) about 5% to about 10% of asolvent selected from isopropanol, ethylene glycol, and butylcellosolve, (c) about 5% to about 25% dibutyl amino ethanol and (d)about 5% to about 20% of a phosphate surfactant.

The phosphate surfactants we prefer are ethoxylated phosphate esters,and their alkali metal salts, of mono- and disubstituted phenols; thesubstitutions on the phenolic moieties are hydrocarbon chains of eightto twelve carbon atoms. The amount or ethoxylation may varyconsiderably, i.e. from one ethoxy unit to ten, fifteen, or more. Someexamples, (including their commercial trademarks of Rhone-Poulenc) are:

1. "RM 510"--Polyoxyethylene dinonyl phenyl ether phosphate CAS RegistryName: poly(oxy 1-2 ethanediyl), alpha (dinonylphenyl) omega hydroxyphosphate

2. "RM 410"--Polyoxyethylene dinonlyphenyl ether phosphate CAS RegistryName: poly(oxy 1-2 ethanediyl), alpha-(dinonylphenyl)-omega hydroxyphosphate

3. "RE 410"--polyoxyethylene nonylphenyl ether phosphate CAS RegistryName: poly(oxy 1-2 ethanediyl) alpha-(nonylphenyl)-omega hydroxy,branched, phosphate

4. "RA 600"--complex alkyl phosphate ester CAS Registry Name: poly(oxy1-2 ethanediyl) alpha omega hydro mono C₈₋₁₀

5. "RE 610"--polyoxyethylene nonlyphenyl, branched phosphate CASRegistry Name: poly(oxy 1-2 ethanediyl) alpha (nonylphenyl) omegahydroxy, branched phosphate.

These phosphate surfactants and similar phosphate surfactants aresometimes referred to herein as "phosphate surfactants".

The efficacy of our composition was demonstrated in a series ofexperiments. The experiments included close, crown and Marsh funneltests for several series of ranges and proportions of the components ofour system.

The procedure was as follows. In each case, 300 ml of clear, dye-free,additive-free Diesel oil was added to a Waring blender. The blenderspeed was set at 1500-1800 rpm using a digital tachometer before theDiesel was added to the blender cup. The Diesel oil was added, theblender started, the gellant (80% active phosphate ester with KOH ifnoted) was added; then the activator (see the definition above) and thestop watch started. Closure is the time for the ball on the bottom ofthe blender to disappear; crowning is the time after closure for thevortex to disappear. After two minutes of mixing, the sample wastransferred to the Marsh funnel and given a 30 seconds rest. Then thesample was permitted to flow through the Marsh funnel and the time thegel takes to reach the 100 ml line on a 300 ml beaker is recorded asMarsh funnel time. A 52 ml sample was then transferred to the Fannviscometer as soon as possible. The Fann viscometer program ran at 40revolutions per second and 100 revolutions per second with a b5 bob.

For each of the tests, a 60% solution of iron sulfate was used. Severalamines with similar molecular weights were mixed with the iron sulfatesolution, which was then placed in hydrocarbon fracturing fluidcontaining 0.5% orthophosphate ester, unless stated otherwise, (and withvarying amounts of KOH as noted) and the rapidity of gellation wasmeasured in terms of the results of close, crown and Marsh funnel tests.The phosphoric acid ester used as the gelling agent in each case was thereaction product of phosphoric acid with C₈₋₁₀ alcohols. These andrelated gelling agents based on phosphoric acid esters are described bySmith and Persinski in U.S. Pat. Nos. 5,417,287, 5,571,315, 5,614,010,and 5,647,900; we may use any of the gelling agents described in thesepatents, which are incorporated herein by reference.. HGA 715 is 80%phosphate ester, 15% of a 45% active solution of KOH, and 5% solvent.

A series of close, crown, and Marsh funnel tests was run to determinethe optimum concentration of DBAE. The results of these tests are shownbelow in Table I, from which it may be seen that 20% DBAE, based on theovarall activator composition, was the optimum concentration. A range of15% to 25% is quite efficient and is a preferred range in our invention.All gels were made at 0.5% gellant and 0.5% activator.

                  TABLE I                                                         ______________________________________                                        5% DBEA 10% DBEA  15% DBEA  20% DBEA                                                                              25% DBEA                                    60% Fe.sub.2 SO.sub.4  60% Fe.sub.2 SO.sub.4  60% Fe.sub.2 SO.sub.4                                             60% Fe.sub.2 SO.sub.4  55% Fe.sub.2                                           SO.sub.4                                    10%          10%         10%        10%        10%                            RM510        RM510       RM510      RM510      RM510                          10% Ipa      10% Ipa     10% Ipa    10% Ipa    10% Ipa                        5% water    10% water    5% water                                             Close:0:19 Close:0.07  Close:0.03  Close 0:03 Close:0:06                      Crown:no   Crown:0:20  Crown:0:07  Crown:0:06 Crown:0:10                      Marsh:0:10 Marsh:0:25  Marsh:1:21  Marsh:2:16 Marsh:8:48                                 MF1hr:0:43  MF1hr:0:54  MF1hr:0:59                               ______________________________________                                    

Then, a series of screenings were run to select a surfactant to furtherenhance the rapidity of gelation Isopropanol is used in combination withthe surfactant, in a ratio of 3:2 to 2:3, preferably 1:1.

                  TABLE II                                                        ______________________________________                                        Surfactant                                                                              Close Time  Crown Time                                                                              Marsh Funnel                                  ______________________________________                                        PL 620    1.49        None      0:07                                            R5 095      None          None        0:02                                    RA 600      0:04          0:06        1:05                                    RB 610      0:07          0:12        2:28                                    RE 510      0:04          0:06        0:06                                    RE 410      0:04          0:06        0:58                                    RM 510      0:04          0:06        1:54                                  ______________________________________                                    

The temperature stability of our gels is shown in FIGS. 1 and 2. FIG. 1shows the results in the Fann Viscometer or 0.5% phosphate ester(neutralized with 15% KOH solution as stated above) and 0.5% activator.The upper edge of the band represents the result at 40 rpm and the loweredge of the band represents the result at 100 rpm. In FIG. 2, 0.3%gelling agent and 0.3% activator were used; again, the higher values areat 40 rpm and the lower ones are at 100 rpm.

An activator formulation comprising 60% iron sulfate (60% conc.), 20%DBAE, and 10% phosphate surfactant (RM 510) was now tested againstphosphate ester compositions having twenty different incremental amountsof KOH neutralizer. These results are shown graphically in FIGS. 3, 4,and 5. An optimum neutralization of the phosphate ester is in the rangeof about 8-18% KOH, taking all three criteria--close time, crown time,and Marsh funnel time--into account, although any amount from 0-20% willhave beneficial effects.

What is claimed is:
 1. An activator composition for gelling hydrocarbonswith phosphate esters, comprising (a) 50% to 80% of a 60% solution ofiron sulfate, (b) 5% to 10% isopropanol, (c) 5% to 25%2-dibutylaminoethanol, and (d) 5% to 20% of a phosphate surfactant. 2.Composition of claim 1 wherein said phosphate surfactant is a phosphateester of ethoxylated dodecylalcohol.
 3. Composition of claim 1 whereinsaid phosphate surfactant is a polyoxyethylene dinonylphenyl etherphosphate.
 4. Composition of claim 1 wherein said 2-dibutylaminoethanolis present in an amount from 15% to 25%.
 5. Composition for activatingphosphate ester gellants for hydrocarbons comprising 30-48 parts byweight iron sulfate, 5-25 parts by weight dibutylaminoethanol, and 5-20parts by weight phosphate surfactant.
 6. Composition of claim 5including a solvent selected from the group consisting of isopropanol,ethylene glycol, and butyl cellosolve.
 7. Composition of claim 5 whereinthe phosphate surfactant is an ethoxylated phosphate ester, or saltthereof, of a mono- or disubstituted phenol wherein the substitutions onthe phenolic moieties are hydrocarbon chains of eight to twelve carbonatoms.
 8. Composition of claim 5 including isopropanol in a weight ratioto said phosphate surfactant of about 3:2 to 2:3.